Renal denervation balloon catheter with ride along electrode support

ABSTRACT

A renal nerve ablation device may include an elongate tubular member having a distal region. An expandable member may be coupled to the distal region. An electrode support may be coupled to the distal region of the elongate tubular member and extend over a body of the expandable member. The electrode support may be free of connection to the body of the expandable member. One or more electrodes may be coupled to the electrode support.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/838,086, filed Jun. 21, 2013, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and methods for using and manufacturing medical devices. More particularly, the present disclosure pertains to medical devices for renal nerve ablation.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed for medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices.

BRIEF SUMMARY

A medical device for renal nerve ablation may include a catheter shaft, an expandable member coupled to the catheter shaft, the expandable member having a proximal region, a distal region, and a body extending therebetween. The medical device may further include an electrode support coupled to the catheter shaft and positioned over the body of the expandable member, the electrode support including a plurality of flexible elongate members and a plurality of electrode assemblies disposed on the elongate members, the electrode support capable of expanding with the expandable member, wherein the electrode support is free from attachment with the body of the expandable member.

A medical device may include a catheter shaft, an expandable balloon, a flexible elongate electrode assembly, and a plurality of electrode elements. The expandable balloon may have a distal waist, proximal waist, and a body extending therebetween, the proximal waist being coupled to the catheter shaft. The flexible elongate electrode assembly may be coupled to the catheter shaft and may extend in a helix over the body of the expandable balloon, the electrode assembly free from attachment to the body of the expandable balloon. The plurality of electrode elements may be disposed on the flexible elongate electrode assembly.

A method for treating hypertension may include providing a medical device, the medical device including a catheter shaft, an expandable member coupled to the catheter shaft, an expandable electrode support coupled to the catheter shaft and positioned over the expandable member, the electrode support including a plurality of flexible elongate members and a plurality of electrode assemblies disposed on the elongate members, the electrode support capable of expanding with the expandable member, wherein the electrode support is free from attachment with the expandable member, and a delivery sheath. The method may further include the steps of advancing the medical device through a blood vessel to a position within a renal artery, expanding the expandable member, thereby expanding the electrode support, energizing the electrode assemblies, collapsing the expandable member, and thereafter, withdrawing the expandable member and the electrode support into the delivery sheath, thereby collapsing the electrode support.

The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of an example renal nerve ablation device;

FIG. 2 is a perspective view of an example expandable member of a renal nerve ablation device;

FIG. 3 is a partial top view of the expandable member of FIG. 2 in an unrolled or flat configuration;

FIG. 4 is a top view of a portion of an example electrode assembly;

FIG. 5 is a partial cross-sectional view A-A of FIG. 4;

FIG. 6 is a partial cross-sectional view B-B of FIG. 4;

FIG. 7 is a perspective view of an example renal nerve ablation device;

FIG. 8 is a perspective view of the electrode support of FIG. 7;

FIG. 9 is a perspective view of an example expandable member;

FIG. 10 is an end view of the expandable member of FIG. 9;

FIG. 11 is a perspective view of the expandable member of FIG. 9 with an electrode support;

FIG. 12 is a perspective view of another example renal nerve ablation device;

FIG. 13 is a partial top view of the electrode support of FIG. 12 in an unrolled or flat configuration;

FIG. 14 is a perspective view of another example renal nerve ablation device; and

FIG. 15 is a perspective view of another example renal nerve ablation device.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DETAILED DESCRIPTION

The following description should be read with reference to the drawings, which are not necessarily to scale, wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings are intended to illustrate but not limit the claimed invention. Those skilled in the art will recognize that the various elements described and/or shown may be arranged in various combinations and configurations without departing from the scope of the disclosure. The detailed description and drawings illustrate example embodiments of the claimed invention.

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.

All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about”, in the context of numeric values, generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term “about” may include numbers that are rounded to the nearest significant figure. Other uses of the term “about” (i.e., in a context other than numeric values) may be assumed to have their ordinary and customary definition(s), as understood from and consistent with the context of the specification, unless otherwise specified.

The recitation of numerical ranges by endpoints includes all numbers within that range, including the endpoints (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it would be within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described, unless clearly stated to the contrary. That is, the various individual elements described below, even if not explicitly shown in a particular combination, are nevertheless contemplated as being combined or arranged with each other to form other additional embodiments or to complement and/or enrich the described embodiment(s), as would be understood by one of ordinary skill in the art.

Certain treatments are aimed at the temporary or permanent interruption or modification of select nerve function. One example treatment is renal nerve ablation, which is sometimes used to treat conditions such as or related to hypertension, congestive heart failure, diabetes, or other conditions impacted by high blood pressure or salt retention. The kidneys produce a sympathetic response, which may increase the undesired retention of water and/or sodium. The result of the sympathetic response, for example, may be an increase in blood pressure. Ablating some of the nerves running to the kidneys (e.g., disposed adjacent to or otherwise along the renal arteries) may reduce or eliminate this sympathetic response, which may provide a corresponding reduction in the associated undesired symptoms (e.g., a reduction in blood pressure).

Some embodiments of the present disclosure relate to a power generating and control apparatus, often for the treatment of targeted tissue in order to achieve a therapeutic effect. In some embodiments, the target tissue is tissue containing or proximate to nerves, including renal arteries and associated renal nerves. In other embodiments the target tissue is luminal tissue, which may further comprise diseased tissue such as that found in arterial disease.

In some embodiments of the present disclosure, the ability to deliver energy in a targeted dosage may be used for nerve tissue in order to achieve beneficial biologic responses. For example, chronic pain, urologic dysfunction, hypertension, and a wide variety of other persistent conditions are known to be affected through the operation of nervous tissue. For example, it is known that chronic hypertension that may not be responsive to medication may be improved or eliminated by disabling excessive nerve activity proximate to the renal arteries. It is also known that nervous tissue does not naturally possess regenerative characteristics. Therefore it may be possible to beneficially affect excessive nerve activity by disrupting the conductive pathway of the nervous tissue. When disrupting nerve conductive pathways, it is particularly advantageous to avoid damage to neighboring nerves or organ tissue. The ability to direct and control energy dosage is well-suited to the treatment of nerve tissue. Whether in a heating or ablating energy dosage, the precise control of energy delivery as described and disclosed herein may be directed to the nerve tissue. Moreover, directed application of energy may suffice to target a nerve without the need to be in exact contact, as would be required when using a typical ablation probe. For example, eccentric heating may be applied at a temperature high enough to denature nerve tissue without causing ablation and without requiring the piercing of luminal tissue. However, it may also be desirable to configure the energy delivery surface of the present disclosure to pierce tissue and deliver ablating energy similar to an ablation probe with the exact energy dosage being controlled by a power control and generation apparatus.

In some embodiments, efficacy of the denervation treatment can be assessed by measurement before, during, and/or after the treatment to tailor one or more parameters of the treatment to the particular patient or to identify the need for additional treatments. For instance, a denervation system may include functionality for assessing whether a treatment has caused or is causing a reduction in neural activity in a target or proximate tissue, which may provide feedback for adjusting parameters of the treatment or indicate the necessity for additional treatments.

While the devices and methods described herein are discussed relative to renal nerve ablation and/or modulation, it is contemplated that the devices and methods may be used in other treatment locations and/or applications where nerve modulation and/or other tissue modulation including heating, activation, blocking, disrupting, or ablation are desired, such as, but not limited to: blood vessels, urinary vessels, or in other tissues via trocar and cannula access. For example, the devices and methods described herein can be applied to hyperplastic tissue ablation, cardiac ablation, pulmonary vein isolation, pulmonary vein ablation, tumor ablation, benign prostatic hyperplasia therapy, nerve excitation or blocking or ablation, modulation of muscle activity, hyperthermia or other warming of tissues, etc.

FIG. 1 is a schematic view of an example renal nerve ablation system 100. System 100 may include a renal nerve ablation device 120. Renal nerve ablation device 120 may be used to ablate nerves (e.g., renal nerves) disposed adjacent to the kidney K (e.g., renal nerves disposed about a renal artery RA). In use, renal nerve ablation device 120 may be advanced through a blood vessel such as the aorta A to a position within the renal artery RA. This may include advancing renal nerve ablation device 120 through a guide sheath or catheter 14. When positioned as desired, renal nerve ablation device 120 may be activated to activate one or more electrodes (not shown). This may include operatively coupling renal nerve ablation device 120 to a control unit 110, which may include an RF generator, so as to supply the desired activation energy to the electrodes. For example, renal nerve ablation device 120 may include a wire or conductive member 18 with a connector 20 that can be connected to a connector 22 on the control unit 110 and/or a wire 24 coupled to the control unit 110. In at least some embodiments, the control unit 110 may also be utilized to supply/receive the appropriate electrical energy and/or signal to activate one or more sensors disposed at or near a distal end of renal nerve ablation device 120. When suitably activated, the electrodes may be capable of ablating tissue (e.g., renal nerves) as described below and the sensors may be used to detect desired physical and/or biological parameters.

An exemplary control unit 110 and associated energy delivery methods useable with the embodiments disclosed herein are disclosed in U.S. Patent Application Publication No. 2012/0095461 entitled “Power Generating and Control Apparatus for the Treatment of Tissue”, the full disclosure of which is incorporated by reference herein. Further examples useable with the embodiments disclosed herein are disclosed in U.S. Pat. No. 7,742,795 entitled “Tuned RF Energy for Selective Treatment of Atheroma and Other Target Tissues and/or Structures”, U.S. Pat. No. 7,291,146 entitled “Selectable Eccentric Remodeling and/or Ablation of Atherosclerotic Material”, and U.S. Patent Application Publication No. 2008/0188912 entitled “System for Inducing Desirable Temperature Effects on Body Tissue”, the full disclosures of which are incorporated herein by reference. In some embodiments, particularly in some embodiments utilizing monopolar energy delivery, the system 100 may also include a ground/common electrode (not shown), which may be associated with the ablation device 120. The ground/common electrode may be a separate pad that is electrically or otherwise operatively coupled to the control unit 110, or otherwise associated with the system 100.

In some embodiments, the control unit 110 may include a processor or otherwise be coupled to a processor to control or record treatment. The processor may typically comprise computer hardware and/or software, often including one or more programmable processor units running machine-readable program instructions or code for implementing some, or all, of one or more of the embodiments and methods described herein. The code may often be embodied in a tangible media such as a memory (optionally a read-only memory, a random access memory, a non-volatile memory, or the like) and/or a recording media (such as a floppy disk, a hard drive, a CD, a DVD, or other optical media, a non-volatile solid-state memory card, or the like). The code and/or associated data and signals may also be transmitted to or from the processor via a network connection (such as a wireless network, an ethernet, an internet, an intranet, or the like), and some or all of the code may also be transmitted between components of a renal nerve ablation system and within the processor via one or more buses, and appropriate standard or proprietary communications cards, connectors, cables, and the like may often be included in the processor. The processor may often be configured to perform the calculations and signal transmission steps described herein at least in part by programming the processor with the software code, which may be written as a single program, a series of separate subroutines or related programs, or the like. The processor may comprise standard or proprietary digital and/or analog signal processing hardware, software, and/or firmware, and may desirably have sufficient processing power to perform the calculations described herein during treatment of the patient, the processor may optionally comprise a personal computer, a notebook computer, a tablet computer, a proprietary processing unit, or a combination thereof. Standard or proprietary input devices (such as a mouse, keyboard, touchscreen, joystick, etc.) and output devices (such as a printer, speakers, display, etc.) associated with modern computer systems may also be included, and processors having a plurality of processing units (or even separate computers) may be employed in a wide range of centralized or distributed data processing architectures.

In some embodiments, control software for the system 100 may use a client-server scheme to further enhance system ease of use, flexibility, and reliability. “Clients” may be the system control logic; “servers” may be the control hardware. A communications manager may deliver changes in system conditions to subscribing clients and servers. Clients may “know” what the present system condition is, and what command or decision to perform based on a specific change in condition. Servers may perform the system function based on client commands. Because the communications manager may be a centralized information manager, new system hardware may not require changes to prior existing client-server relationships; new system hardware and its related control logic may then merely become an additional “subscriber” to information managed through the communications manager. This control schema may provide the benefit of having a robust central operating program with base routines that are fixed; no change to base routines may be necessary in order to operate new circuit components designed to operate with the system.

In some embodiments, the renal nerve ablation device 120 may include an elongate tubular member or catheter shaft 122, as shown in FIG. 2. In some embodiments, the elongate tubular member or catheter shaft 122 may be configured to be slidingly advanced over a guidewire or other elongate medical device to a target site. In some embodiments, the elongate tubular member or catheter shaft 122 may be configured to be slidingly advanced within a guide sheath or catheter 14 to a target site. In some embodiments, the elongate tubular member or catheter shaft 122 may be configured to be advanced to a target site over a guidewire, within a guide sheath or catheter 14, or a combination thereof.

An expandable member 130 may be disposed at, on, about, or near a distal region of the elongate tubular member or catheter shaft 122. The expandable member 130 may have a body 135, a proximal waist 136, and a distal waist 137. In some embodiments, the expandable member 130 may be fixedly attached to the elongate tubular member or catheter shaft 122. In some embodiments the proximal waist 136 and the distal waist 137 are attached to the catheter shaft 122 while the body 135 is free from attachment to the catheter shaft 122. In some embodiments, the expandable member 130 may be self-expanding from a collapsed delivery state to an expanded state, such as a basket, a swellable foam or other material, or a plurality of struts, for example. In some embodiments, the expandable member 130 may be selectively expanded from a collapsed delivery state to an expanded state, such as a compliant, non-compliant, or semi-compliant balloon, for example. In some embodiments, one or more electrodes may be disposed on, disposed about, or coupled to an outer surface of the expandable member 130. In some embodiments, the one or more electrodes may be operatively and/or electrically connected to the control unit 110 and/or the RF generator. In some embodiments, the one or more electrodes may include a plurality of electrode assemblies. In some embodiments, one or more of the plurality of electrode assemblies may be configured to be monopolar or bipolar, and may further include a temperature sensor, for example, a thermistor or thermocouple.

For example, as shown in FIG. 2, in some embodiments, the electrode assemblies may be arranged on the expandable member 130, shown here in an expanded state, according to a plurality of generally cylindrical treatment zones A-D. In other embodiments, the expandable member 130 or other components of the treatment system may include additional electrode assemblies that are not in a treatment zone or are otherwise not used or configured to deliver a treatment energy.

The treatment zones A-D and associated electrode assemblies 140 a-d are further illustrated in FIG. 3, which is an “unrolled” depiction of a portion of the expandable member 130 of FIG. 2. In some embodiments, the expandable member may be a balloon with a 4 mm diameter and two electrode assemblies 140 a-b. In other embodiments, the expandable member may be a balloon with a 5 mm diameter and three electrode assemblies 140 a-c. In some embodiments, the expandable member may be a balloon with a 6, 7, or 8 mm diameter and four electrode assemblies 140 a-d, as depicted in FIG. 2. For any of these configurations, the expandable member may have a working length of about 10 mm to about 100 mm, or about 18 mm to about 25 mm, which may be the approximate longitudinal span of all the treatment zones A-D shown in FIGS. 2 and 3. The electrode assemblies 140 a-d may be attached to a balloon using adhesive, or other suitable means.

Returning to FIG. 2, the treatment zones A-D may be longitudinally adjacent to one another along longitudinal axis L-L, and may be configured such that energy applied by the electrode assemblies create treatments that do not overlap. Treatments applied by the longitudinally adjacent bipolar electrode assemblies 140 a-d may be circumferentially non-continuous along longitudinal axis L-L. For example, with reference to FIG. 3, lesions created in treatment zone A may in some embodiments minimize overlap about a circumference (laterally with respect to L-L in this view) with lesions created in treatment zone B. In other embodiments, however, the energy applied by the electrode assemblies, such as the electrode assemblies shown in FIG. 3, may overlap, longitudinally, circumferentially, and/or in other ways, to at least some extent.

Whether or not treatment zones between electrodes/electrode pairs will overlap may be influenced by a wide variety of factors, including, but not limited to, electrode geometry, electrode placement density, electrode positioning, ground/common electrode(s) placement and geometry (in monopolar embodiments), energy generator output settings, output voltage, output power, duty cycle, output frequency, tissue characteristics, tissue type, etc. In some embodiments, individual electrodes of a bipolar electrode pair may each define its own treatment zone, and such treatment zones may partially or entirely overlap. In some embodiments, the overlap of treatment zones may extend substantially continuously around a circumference of the expandable member and/or around a circumference in a tissue surrounding a body passageway. In other embodiments, there may be overlap in treatment zones, however, that overlap may not be substantially continuous around a circumference and significant discontinuities in the treatment zones may be present.

Returning to FIG. 3, each electrode pad assembly may include four major elements, which are a distal electrode pad 150 a-d, intermediate tail 160 a-d, proximal electrode pad 170 a-d, and proximal tail 180 b,d (not shown for electrode pad assemblies 140 b and 140 c). Constructional details of the electrode assemblies 140 a-d are shown and described with reference to FIGS. 4-6.

FIG. 4 shows a top view of electrode assembly 200, which is identified in FIG. 3 as electrode assembly 140. The electrode assembly 200 may be constructed as a flexible circuit having a plurality of layers. Such layers may be continuous or non-contiguous, i.e., made up of discrete portions. Shown in FIGS. 5 and 6, a base layer 202 of insulation may provide a foundation for the electrode assembly 200. The base layer 202 may be constructed from a flexible polymer such as polyimide, although other materials are contemplated. In some embodiments, the base layer 202 may be from about 0.01 mm thick to about 0.02 mm thick. In some embodiments, the base layer 202 may be approximately 0.5 mil (0.0127 mm) thick. A conductive layer 204 made up of a plurality of discrete traces may be layered on top of the base layer 202. The conductive layer 204 may be, for example, a layer of electrodeposited copper. Other materials are also contemplated. In some embodiments, the conductive layer 204 may be from about 0.01 mm thick to about 0.02 mm thick. In some embodiments, the conductive layer 204 may be approximately 0.5 mil (0.018 mm) thick. An insulating layer 206 may be discretely or continuously layered on top of the conductive layer 204, such that the conductive layer 204 may be fluidly sealed between the base layer 202 and the insulating layer 206. Like the base layer 202, the insulating layer 206 may be constructed from a flexible polymer such as polyimide, although other materials are contemplated. In some embodiments, the insulating layer 206 may be from about 0.01 mm thick to about 0.02 mm thick. In some embodiments, the insulating layer 206 may be approximately 0.5 mil (0.0127 mm) thick. In other embodiments, the insulating layer 206 may be a complete or partial polymer coating, such as PTFE or silicone. Other materials are also contemplated.

The electrode assembly 200 shown in FIG. 4 may include a distal electrode pad 208. In this region, the base layer 202 may form a rectangular shape. This is not intended to be limiting. Other shapes are contemplated. As shown, the electrode assembly 200 may include a plurality of openings to provide for added flexibility, and the pads and other portions of the assemblies may include rounded or curved corners, transitions and other portions. In some instances, the openings and rounded/curved features may enhance the assembly's resistance to delamination from its expandable device, as may occur, in some instances, when the expandable device is repeatedly expanded and collapsed (which may also entail deployment from and withdrawal into a protective sheath), such as may be needed when multiple sites are treated during a procedure.

The distal electrode pad 208 may include a plurality of discrete traces layered on top of the base layer 202. These traces may include a ground trace 210, an active electrode trace 212, and a sensor trace 214. The ground trace 210 may include an elongated electrode support 216 laterally offset from a sensor ground pad 218. The sensor ground pad 218 may be electrically coupled to the elongated electrode support 216 of the ground trace 210 and may be centrally located on the distal electrode pad 208. A bridge 220 may connect a distal most portion of the sensor ground pad 218 to a distal portion of the elongated electrode support 216 of the ground trace 210. The bridge 220 may taper down in width as it travels to the sensor ground pad 218. In some embodiments, the bridge 220 may have a relatively uniform and thin width to enable a desired amount of flexibility. The elongated electrode support 216 may taper down in width at its proximal end, however, this is not required. In some embodiments, the elongated electrode support 216 may abruptly transition to a much thinner trace at its proximal portion, to enable a desired amount of flexibility. Generally, the curvature of the traces where necking is shown may be optimized to reduce balloon recapture forces and the potential for any snagging that sharper contours may present. The shape and position of the traces may also be optimized to provide dimensional stability to the electrode assembly 200 as a whole, so as to prevent distortion during deployment and use.

The ground trace 210 and active electrode trace 212 of FIG. 4 may share a similar construction. The active electrode trace 212 may also include an elongated electrode support 216.

FIG. 5 shows a partial cross-section A-A of the distal electrode pad 208. An electrode 222 is shown layered over a portion of the insulating layer 206, which may have a plurality of passages (e.g., holes) to enable the electrode 222 to couple to the elongated electrode support 216 of the ground trace 210 (of conductive layer 204).

As shown in FIG. 4, the ground electrode trace 210 and active electrode trace 212 may include a plurality of electrodes. Three electrodes 222 may be provided for each electrode trace, however, more or less may be used. Additionally, each electrode 222 may have radiused corners to reduce tendency to snag on other devices and/or tissue. Although the above description of the electrodes 222 and the traces associated with them has been described in the context of a bi-polar electrode assembly, those of skill in the art will recognize that the same electrode assembly may function in a monopolar mode as well. For instance, as one non-limiting example, the electrodes associated with active electrode traces 212 and 242 may be used as monopolar electrodes, with ground trace 210 disconnected during energization of those electrodes.

In some embodiments, as shown in FIG. 4 for example, each electrode 222 may be approximately 1.14 mm by 0.38 mm, with approximately 0.31 mm gaps lying between the electrodes 222. The electrodes 222 of the ground trace 210 and active electrode trace 212 may be laterally spaced by approximately 1.85 mm. In some embodiments, as shown in FIG. 5 for example, the electrodes 222 may be gold pads approximately 0.038 mm thick from the conductive layer 204 and that may protrude about 0.025 mm above the insulating layer 206. Without limiting the use of other such suitable materials, gold may be a good electrode material because it is very biocompatible, radiopaque, and electrically and thermally conductive. In other embodiments, the electrode thickness of the conductive layer 204 may range from about 0.030 mm to about 0.051 mm. At such thicknesses, relative stiffness of the electrodes 222, as compared to, for example, the copper conductive layer 204, may be high. Because of this, using a plurality of electrodes, as opposed to a single electrode, may increase flexibility. In other embodiments, the electrodes may be as small as about 0.5 mm by about 0.2 mm or as large as about 2.2 mm by about 0.6 mm for electrode 222.

While it may be an important design optimization consideration to balance the thickness of the gold above the insulating layer 206 so as to achieve good flexibility while maintaining sufficient height so as to provide good tissue contact, this may be counterbalanced with the goal of avoiding a surface height that may snag during deployment or collapse of the balloon. These issues may vary according to other elements of a particular procedure, such as balloon pressure. For many embodiments, it has been determined that electrodes that protrude approximately 0.025 mm above the insulating layer 206 will have good tissue contact at balloon inflation pressures below 10 atm and as low as 2 atm. These pressures may be well below the typical inflation pressure of an angioplasty balloon.

The sensor trace 214 may be centrally located on the distal electrode pad 208 and may include a sensor power pad 224 facing the sensor ground pad 218. These pads may connect to power and ground poles of a temperature sensor 226, such as a thermocouple (for example, Type T configuration: Copper/Constantan) or thermistor, as shown in the partial cross-section depicted in FIG. 6.

The temperature sensor 226 may be proximately connected to the sensor power pad 224 and may be distally connected to the sensor ground pad 218. To help reduce overall thickness, the temperature sensor 226 may be positioned within an opening within the base layer 202. In some embodiments, the temperature sensor 226 may be a thermistor having a thickness of about 0.1 mm, which is unusually thin—approximately two-thirds of industry standard. As shown, the temperature sensor 226 may be on a non-tissue contacting side of the distal electrode pad 208. Accordingly, the temperature sensor 226 may be captured between the electrode structure and a balloon when incorporated into a final device, such as ablation device 120. This may be advantageous since surface-mounted electrical components, like thermistors, typically have sharp edges and corners, which may get caught on tissue and possibly cause problems in balloon deployment and/or retraction. This arrangement may also keep soldered connections from making contact with blood, since solder is typically non-biocompatible. Further, due to the placement of the temperature sensor, it may measure temperature representative of tissue and the electrodes 222.

From the distal electrode pad 208, the combined base layer 202, conductive layer 204, and insulating layer 206 may reduce in lateral width to an intermediate tail 228. Here, the conductive layer 204 may be formed to include an intermediate ground line 230, intermediate active electrode line 232, and intermediate sensor line 234, which may be respectively coextensive traces of the ground trace 210, active electrode trace 212, and sensor trace 214 of the distal electrode pad 208.

From the intermediate tail 228, the combined base layer 202, conductive layer 204, and insulating layer 206 may increase in lateral width to form a proximal electrode pad 236. The proximal electrode pad 236 may be constructed similarly to the distal electrode pad 208, with the electrode geometry and temperature sensor arrangement being essentially identical, although various differences may be present. However, as shown, the proximal electrode pad 236 may be laterally offset from the distal electrode pad 208 with respect to a central axis G-G extending along the intermediate ground line 230. The intermediate active electrode line 232 and intermediate sensor line 234 may be laterally coextensive with the proximal electrode pad 236 on parallel respective axes with respect to central axis G-G.

From the proximal electrode pad 236, the combined base layer 202, conductive layer 204, and insulating layer 206 may reduce in lateral width to form a proximal tail 238. The proximal tail 238 may include a proximal ground line 240, proximal active electrode line 242, and proximal sensor line 244, as well the intermediate active electrode line 232 and intermediate sensor line 234. The proximal tail 238 may include connectors (not shown) to enable coupling to one or more sub-wiring harnesses and/or connectors and ultimately to control unit 110. Each of these lines may be extended along parallel respective axes with respect to central axis G-G.

As shown, the electrode assembly 200 may have an asymmetric arrangement of the distal electrode pad 208 and proximal electrode pad 236, about axis G-G. Further, the ground electrodes of both electrode pads may be substantially aligned along axis G-G, along with the intermediate and proximal ground lines 230/240. It has been found that this arrangement may present certain advantages. For example, by essentially sharing the same ground trace, the width of the proximal tail may be only about one and a half times that of the intermediate tail 228, rather than being approximately twice as wide if each electrode pad had independent ground lines. Thus, the proximal tail 238 may be narrower than two of the intermediate tails 228.

Further, arranging the electrode pads to share a ground trace may allow control of which electrodes will interact with each other. This may not be immediately apparent when viewing a single electrode assembly, but may become evident when more than one electrode assembly 200 is assembled onto an expandable member, such as a balloon, for example as shown in FIG. 3. The various electrode pads may be fired and controlled using solid state relays and multiplexing with a firing time ranging from about 100 microseconds to about 200 milliseconds or about 10 milliseconds to about 50 milliseconds. For practical purposes, the electrode pads may appear to be simultaneously firing yet stray current between adjacent electrode pads of different electrode assemblies 200 may be prevented by rapid firing of electrodes in micro bursts. This may be performed such that adjacent electrode pads of different electrode pad assemblies 200 are fired out of phase with one another. Thus, the electrode pad arrangement of the electrode assembly may allow for short treatment times—about 10 minutes or less of total electrode firing time, with some approximate treatment times being as short as about 10 seconds, with an exemplary embodiment being about 30 seconds. Some benefits of short treatment times may include minimization of post-operative pain caused when nerve tissue is subject to energy treatment, shortened vessel occlusion times, reduced occlusion side effects, and quick cooling of collateral tissues by blood perfusion due to relatively minor heat input to luminal tissue.

In some embodiments, the common ground may typically carry 200 VAC at 500 kHz coming from the negative electrode pole, and a 1V signal from the temperature sensor 226 (in the case of a thermistor) that may require filtering of the RF circuit such that the thermistor signal may be sensed and used for generator control. In some embodiments, because of the common ground, the thermistor of the adjacent electrode pair may be used to monitor temperature even without firing the adjacent electrode pair. This may provide the possibility of sensing temperatures proximate to both the distal electrode pad 208 and the proximal electrode pad 236, while firing only one of them.

Referring again to FIG. 3, the electrode pad arrangement of each electrode assembly 140 a-d may also enable efficient placement on the expandable member 130. As shown, the electrode assemblies 140 a-d may “key” into one another to enable maximum use of the expandable member surface area. This may be accomplished in part by spacing the electrode pads apart by setting the longitudinal length of each intermediate tail. For example, the intermediate tail length electrode assembly 140 a may be set to a distance that separates its distal and proximal electrode pads 150 a, 170 a such that the laterally adjacent proximal electrode pad 170 b of the laterally adjacent electrode pad assembly 140 b keys next to the intermediate tail 160 a of electrode pad assembly 140 a. Further, the distal electrode pad 150 a of electrode assembly 140 a may be keyed between the intermediate tail 160 b of electrode assembly 140 b and the intermediate tail 160 d of electrode assembly 140 d. Thus, the length of each intermediate tail 160 a-d may also require each electrode pad of any one electrode assembly to be located in non-adjacent treatment zones.

Expandable member or balloon surface area maximization may also be enabled in part by laterally offsetting both electrode pads of each electrode assembly 140 a-d. For example, the rightwards lateral offset of each distal electrode pad 150 a-d and the leftwards lateral offset of the proximal electrode pad 170 a-d allow adjacent electrode pad assemblies to key into one another such that some of the electrode pads may laterally overlap one another. For example, the distal electrode pad 150 a of electrode assembly 140 a may laterally overlap with proximal electrode pad 170 b of electrode assembly 140 b. Further, the distal electrode pad 150 b of electrode assembly 140 b may laterally overlap with the proximal electrode pad 170 c of electrode assembly 140 c. However, the length of each intermediate tail may prevent circumferential overlap (longitudinal overlap in this view) of the electrode pads, thus maintaining the non-contiguous nature of the treatment zones in the longitudinal direction L-L.

The arrangement and geometry of the electrode pads, as well as the arrangement and geometry of the tails of the flexible circuits may also facilitate folding or otherwise collapsing the balloon into a relatively compact un-expanded state. For instance, in embodiments with an expanded diameter of up to about 10 mm, the device in an un-expanded state may have as low as an about 1 mm diameter.

Some embodiments may utilize a standard electrode assembly having identical dimensions and construction, wherein the number and relative position of electrode assemblies on an outer surface of an expandable member or a balloon becomes a function of the expandable member or balloon diameter and/or length while electrode assembly geometries remain unchanged amongst various expandable member or balloon sizes. The relative positioning of electrode assemblies relative to the expandable member or balloon diameter and/or length may then be determined by the desired degree or avoidance of circumferential and/or axial overlap of adjacent electrode pads of neighboring electrode assemblies on an expandable member or a balloon of a given size. In other embodiments, however, all of the electrode assemblies on the expandable member or balloon may not necessarily be identical.

The system 100 may be used to perform a method of treatment in accordance with one non-limiting embodiment of the disclosure. For example, the control unit 110 may be operationally coupled to the ablation device 120, which may be inserted into a body passageway such that an expandable member 130 (having a plurality of electrode assemblies) may be placed adjacent to a first section of the body passageway where therapy is required. Placement of the ablation device 120 at the first section of the body passageway where therapy is required may be performed according to conventional methods, e.g., over a guidewire under fluoroscopic guidance. Once inserted, the expandable member 130 may be made to expand from a collapsed delivery configuration to an expanded configuration, for example by pressurizing fluid from about 2-10 atm in the case of a balloon. This may cause the electrodes and/or electrode assemblies of the expandable member 130 to come into contact with the first section of the body passageway.

In some embodiments, the control unit 110 may measure impedance at the electrode assemblies to confirm apposition of the electrodes with the body passageway. In at least some of these embodiments, the treatment may proceed even if apposition is not sensed for all of the electrodes. For instance, in some embodiments, the treatment may proceed if apposition is sensed for 50% or more of the electrodes, and may allow for less than complete uniformity of apposition circumferentially and/or axially. For example, in some instances the catheter may be positioned such that one or more of the proximal electrodes are in the aorta A and exposed to blood, and impedance sensed for such electrodes may not fall within a pre-designated range (such as, for example, 500-1600 ohms), indicating an absence of tissue apposition for those electrodes. In some instances, the system may allow for user authorization to proceed with the treatment even if there is less than uniform electrode/tissue apposition. Subsequently, the control unit 110 may activate the electrodes to create a corresponding number of lesions. During activation of the electrodes, the control unit 110 may use temperature sensors of the electrode pads to monitor heat of the electrode and/or the tissue. In this manner, more or less power may be supplied to each electrode pad as needed during treatment.

In some embodiments, the control unit 110 may apply a uniform standard for determining apposition to all the electrodes of the ablation device 120. For instance, the control unit 110 may utilize the same pre-designated range of resistance measurements to all of the electrodes. In other instances, however, including some, although not all, monopolar applications, different standards may be applied to different monopolar electrodes for determining apposition. For example, in some monopolar embodiments, each monopolar electrode may define a discrete electrical circuit through the tissue to the common/indifferent electrode (or electrodes), and the characteristics of those circuits (e.g. resistance) may vary significantly based on the distance between the monopolar electrode and common electrode, the tissue characteristics therebetween, and other geometries and characteristics of the device and surrounding tissue. As such, in at least some embodiments, it may be desirable to apply criteria for determining apposition that varies depending on, e.g., the distance between the monopolar electrode and a common ground electrode (e.g. the greater the distance between the two electrodes, the higher the impedance measurement required to determine good apposition). In other embodiments, however, the variance due to these differences in distance and other geometries may be minimal or non-substantive, and a uniform standard may be applied.

After the prescribed therapy in the first section of the body passageway is complete, the expandable member 130 may then be collapsed and moved to an untreated second section of the body passageway where therapy is required to repeat the therapy applied in the first section of the body passageway, and similarly to other sections as needed. The sections may be directly adjacent, or may be separated or spaced apart by some distance.

In some instances, alternative methods will be utilized. For instance, in some embodiments, the treatment may be performed at only a single location in the body passageway, and it may not be necessary to move the expandable member to multiple locations in the body passageway.

Referring to an example of renal hypertension involving the reduction of excessive nerve activity, the system 100 may be used to effect a non-piercing, non-ablating way to direct energy to affect nerve activity. Accordingly, the body passageway may be a renal artery surrounded by nervous tissue. Electrodes on the expandable member 130 may be powered to deliver energy in the known direction of a nerve to be affected, the depth of energy penetration being a function of energy dosage, electrode type (e.g. monopolar vs. bipolar) and electrode geometry. U.S. Patent Application Publication No. 2008/0188912 entitled “System for Inducing Desirable Temperature Effects on Body Tissue”, the full disclosure of which is incorporated herein by reference, describes some considerations for electrode geometry and the volume of tissue treatment zones that may be taken into account in some, although not necessarily all, embodiments. In some instances, empirical analysis may be used to determine the impedance characteristics of nervous tissue such that the ablation device 120 may be used to first characterize and then treat tissue in a targeted manner. The delivery and regulation of energy may further involve accumulated damage modeling, as well.

As shown, each lesion may be created in a corresponding treatment zone A-D of the expandable member 130. Accordingly, any lesion made in one particular treatment A-D zone may not circumferentially overlap with a lesion of an adjacent treatment zone A-D at any point along the operational axis O-O. In some embodiments, a treatment zone of the expandable member 130 may have more than one electrode pad, and thus in such cases, lesions created by those electrode pads may circumferentially overlap. In those cases, more lesions may be required for a particular anatomy or a pair of electrode pads may be required for performing a diagnostic routine before therapy is applied. Regardless, circumferential overlap of electrodes of adjacent treatment zones may not be present.

Depending on the particular remodeling effect required, the control unit may energize the electrodes with about 0.25 to about 5 Watts average power for about 1 to about 180 seconds, or with about 0.25 to about 900 Joules. Higher energy treatments may be done at lower powers and longer durations, such as 0.5 Watts for 90 seconds or 0.25 Watts for 180 seconds. In monopolar embodiments, the control unit may energize the electrodes with up to 30 Watts for up to 5 minutes, depending on electrode configuration and distance between the electrodes and the common ground. A shorter distance may provide for lower energy for a shorter period of time because energy travels over more localized area with fewer conductive losses. In an example embodiment for use in renal denervation, energy may be delivered for about 30 seconds at a treatment setting of about 5 Watts, such that treatment zones may be heated to about 68° C. during treatment. As stated above, power requirements may depend heavily on electrode type and configuration. Generally, with wider electrode spacing, more power may be required, in which case the average power could be higher than 5 Watts, and the total energy could exceed 45 Joules. Likewise, using a shorter or smaller electrode pair may require scaling the average power down, and the total energy could be less than 4 Joules. The power and duration may be, in some instances, calibrated to be less than enough to cause severe damage, and particularly less than enough to ablate diseased tissue within a blood vessel. The mechanisms of ablating atherosclerotic material within a blood vessel have been well described, including by Slager et al. in an article entitled, “Vaporization of Atherosclerotic Plaque by Spark Erosion” in J. of Amer. Cardiol. (June, 1985), on pp. 1382-6; and by Stephen M. Fry in “Thermal and Disruptive Angioplasty: a Physician's Guide”; Strategic Business Development, Inc., (1990), the full disclosure of which is incorporated herein by reference.

In some embodiments, energy treatments applied to one or both of the patient's renal arteries may be applied at higher levels than would be possible in other passageways of the body without deleterious effects. For instance, peripheral and coronary arteries of the body may be susceptible to a deleterious long-term occlusive response if subjected to heating above a certain thermal response limit. It has been discovered that renal arteries, however, can be subjected to heating above such a thermal response limit without deleterious effect.

In some embodiments, the electrode(s) described herein may be energized to assess and then selectively treat targeted tissue to achieve a desired therapeutic result by a remodeling of the treated tissue. For example, tissue signature may be used to identify tissue treatment regions with the use of impedance measurements. Impedance measurements utilizing circumferentially spaced electrodes within a body passage may be used to analyze tissue. Impedance measurements between pairs of adjacent electrodes may differ when the current path passes through diseased tissue, and when it passes through healthy tissues of a luminal wall, for example. Hence, impedance measurements between the electrodes on either side of diseased tissue may indicate a lesion or other type of targeted tissue, while measurements between other pairs of adjacent electrodes may indicate healthy tissue. Other characterization, such as intravascular ultrasound, optical coherence tomography, or the like, may be used to identify regions to be treated either in conjunction with, or as an alternative to, impedance measurements. In some instances, it may be desirable to obtain baseline measurements of the tissues to be treated to help differentiate adjacent tissues, as the tissue signatures and/or signature profiles may differ from person to person. Additionally, the tissue signatures and/or signature profile curves may be normalized to facilitate identification of the relevant slopes, offsets, and the like between different tissues. Impedance measurements may be achieved at one or more frequencies, ideally two different frequencies (low and high). Low frequency measurement may be done in range of about 1-10 kHz, or about 4-5 kHz and high frequency measurement may be done in range of about 300 kHz-1 MHz, or between about 750 kHz-1 MHz. Lower frequency measurement mainly represents the resistive component of impedance and may correlate closely with tissue temperature where higher frequency measurement may represent the capacitive component of impedance and may correlate with destruction and changes in cell composition.

Phase angle shift between the resistive and capacitive components of impedance may also occur due to peak changes between current and voltage as result of capacitive and resistive changes of impedance. The phase angle shift may also be monitored as means of assessing tissue contact and lesion formation during RF denervation.

In some embodiments, remodeling of a body lumen or passageway may be performed by gentle heating in combination with gentle or standard dilation. For example, an angioplasty balloon catheter structure having electrodes disposed thereon may apply electrical potentials to the vessel wall before, during, and/or after dilation, optionally in combination with dilation pressures which are at or significantly lower than standard, unheated angioplasty dilation pressures. Where balloon inflation pressures of 10-16 atmospheres may, for example, be appropriate for standard angioplasty dilation of a particular lesion, modified dilation treatments combined with appropriate electrical potentials (through flexible circuit electrodes on the balloon, electrodes deposited directly on the balloon structure, or the like) described herein may employ from about 10-16 atmospheres or may be effected with pressures of about 6 atmospheres or less, and possibly as low as about 1 to 2 atmospheres. Such moderate dilation pressures may (or may not) be combined with one or more aspects of the tissue characterization, tuned energy, eccentric treatments, and other treatment aspects described herein for treatment of body lumens, the circulatory system, and diseases of the peripheral vasculature.

In many embodiments, gentle heating energy added before, during, and/or after dilation of a body passageway may increase dilation effectiveness while lowering complications. In some embodiments, such controlled heating with a balloon may exhibit a reduction in recoil, providing at least some of the benefits of a stent-like expansion without the disadvantages of an implant. Benefits of the heating may be enhanced (and/or complications inhibited) by limiting heating of the adventitial layer below a deleterious response threshold. In many cases, such heating of the intima and/or media may be provided using heating times of less than about 10 seconds, often being less than 3 (or even 2) seconds. In other cases, very low power may be used for longer durations. Efficient coupling of the energy to the target tissue by matching the driving potential of the circuit to the target tissue phase angle may enhance desirable heating efficiency, effectively maximizing the area under the electrical power curve. The matching of the phase angle need not be absolute, and while complete phase matching to a characterized target tissue may have benefits, alternative systems may pre-set appropriate potentials to substantially match typical target tissues; though the actual phase angles may not be matched precisely, heating localization within the target tissues may be significantly better than using a standard power form.

In some embodiments, monopolar (unipolar) RF energy application may be delivered between any of the electrodes on the expandable member and a common ground or return electrode positioned on the outside skin or on the device itself. Monoploar RF may be desirable in areas where deep lesions are required. For example, in a monopolar application, each electrode pair may be powered with positive polarity rather than having one positive pole and one negative pole per pair. In some embodiments, a combination of monopolar and bipolar RF energy application may be done where lesions of various depth/size can be selectively achieved by varying the polarity of the electrodes of the pair.

The application of RF energy may be controlled so as to limit a temperature of target and/or collateral tissues, for example, limiting the heating of target tissue such that neither the target tissue nor the collateral tissue sustains irreversible thermal damage. In some embodiments, the surface temperature range may be from about 50° C. to about 90° C. For gentle heating, the surface temperature may range from about 50° C. to about 70° C., while for more aggressive heating, the surface temperature may range from about 70° C. to about 90° C. Limiting heating so as to inhibit heating of collateral tissues to less than a surface temperature in a range from about 50° C. to about 70° C., such that the bulk tissue temperature remains mostly below about 50° C. to about 55° C., may inhibit an immune response that might otherwise lead to stenosis, thermal damage, or the like. Relatively mild surface temperatures between about 50° C. and about 70° C. may be sufficient to denature and break protein bonds during treatment, immediately after treatment, and/or more than one hour, more than one day, more than one week, or even more than one month after the treatment through a healing response of the tissue to the treatment so as to provide a bigger vessel lumen and improved blood flow.

In some embodiments, the target temperature may vary during the treatment, and may be, for instance, a function of treatment time. One possible target temperature profile may include a treatment with a duration of 30 seconds and a twelve second ramp up from nominal body temperature to a maximum target temperature of about 68° C. During the twelve second ramp up phase, the target temperature profile may be defined by a quadratic equation in which target temperature (T) is a function of time (t). The coefficients of the equation may be set such that the ramp from nominal body temperature to about 68° C. may follow a path analogous to the trajectory of a projectile reaching the maximum height of its arc of travel under the influence of gravity. In other words, the ramp may be set such that there may be a constant deceleration in the ramp of temperature (d²T/dt²) and a linearly decreasing slope (dT/dt) in the temperature increase as 12 seconds and 68° C. are reached. Such a profile, with its gradual decrease in slope as it approaches 68° C., may facilitate minimizing over and/or undershoot of the set target temperature for the remainder of the treatment. In some embodiments, the target temperature profile may be equally suitable for bipolar or monopolar treatments, although, in at least some monopolar embodiments, treatment time may be increased. Other target temperature profiles utilizing different durations of time (i.e., 3 seconds, 5 seconds, 8 seconds, 12 seconds, 17 seconds, etc.) and set target temperatures (55° C., 60° C., 65° C., 70° C., 75° C., etc.) in various combinations may be used as desired. For each of the target temperature profiles considered, a temperature ramp embodying or approximating a quadratic equation may be utilized, however, any function or other profile that efficiently heats tissue, optimizes treatment time, and avoids thermal damage to target tissue may be used. However, in still other embodiments, it will not be necessary to utilize a temperature profile that achieves all of these goals. For instance and without limitation, in at least some embodiments, optimization of treatment time may not be essential.

A control method may be executed using the processing functionality of the control unit 110 of FIG. 1 and/or control software, described in further detail above, or in other manners. In at least some instances, the control method may provide for fine regulation of temperature or other treatment parameter(s) at the various treatment sites of the device, while utilizing a relatively simple and robust energy generator to simultaneously energize several of the electrodes or other delivery sites at a single output setting (e.g. voltage), which may minimize cost, size and complexity of the system. The control method may minimize deviation from target temperature or other treatment parameter(s), and hence minimize variation in demand on the energy generator (e.g. voltage demand) during any time slice of the treatment.

In some embodiments, it may be desirable to regulate the application of RF or other energy based on target temperature profiles such as those described above to provide for a gentle, controlled, heating that avoids application of high instantaneous power and, at a microscopic level, associated tissue searing or other damage, which could undesirably result in heat block or otherwise cause a net reduction in thermal conduction heat transfer at the device/tissue interface. In other words, by avoiding higher swings in temperature and the resultant heavier instantaneous application of energy to reestablish temperature near the target temperature, tissue integrity at the immediate interface location may be preserved. Tissue desiccation may result in a net loss of thermal conductivity, resulting in reduced effective transfer of gentle, therapeutic delivery of energy to target tissues beyond the electrode/tissue interface.

Those of skill in the art will appreciate that although a particular control method may be presented for purposes of illustration in the context of the particular electrosurgical devices already described above, that these control methods and similar methods could be beneficially applied to other electro-surgical devices.

In general, the control method may seek to maintain the various treatment sites at a pre-defined target temperature, such as at one of the target temperature profiles discussed above. In some embodiments, the control method may maintain the treatment site(s) at the pre-defined target temperature primarily by regulating output voltage of the RF generator and determining which of the electrodes will by energized at a given time slice (e.g. by switching particular electrodes on or off for that cycle).

The output setting of the generator and switching of the electrodes may be determined by a feedback loop that takes into account measured temperature as well as previous desired output settings. During a particular treatment cycle (e.g. a 25 millisecond slice of the treatment), each of the electrodes may be identified for one of three states: off, energized, or measuring. In some embodiments, electrodes may only be in energized and/or measuring states (an electrode that is energized may also be measuring) if they meet certain criteria, with the default electrode state being off Electrodes that have been identified as energized or measuring electrodes may have voltage applied or be detecting temperature signals for a portion of the cycle, or for the entire cycle.

In some embodiments, the control method may be designed to keep as many candidate electrodes as possible as close to target temperature as possible while minimizing variations in temperature and hence minimizing variations in voltage demand from treatment cycle to treatment cycle.

Each electrode may be initially set to off. At a next step, one of the electrodes may be designated as a primary electrode for that treatment cycle. As discussed in further detail below, during the treatment, the primary electrode designated may vary from treatment cycle to treatment cycle (e.g. cycle through all of the available electrodes). The determination of which electrode may be designated as the primary electrode may be done by accessing a look-up table or using any other suitable functionality for identifying a primary electrode and varying the choice of primary electrode from treatment cycle to treatment cycle.

Additionally, at the next step discussed above, additional electrodes may also be designated as candidate electrodes for energization and/or measuring during that treatment cycle. The additional electrodes designated may be candidates by virtue of being in a certain relationship or lacking a certain relationship relative to the designated primary electrode for that treatment cycle.

For instance, in some bipolar electrode embodiments, some of the electrodes on the ablation device may be arranged in a manner such that there may be a potential for current leakage between the primary electrode and those other electrodes if both the primary electrode and those additional electrodes are energized simultaneously in a treatment cycle, which may undesirably cause interference with the temperature measurement by the associated temperature sensor, imprecision in the amount of energy delivered at each electrode, or other undesirable consequences. For instance, in the embodiment illustrated in FIG. 3, if electrode pad 150 c is designated as a primary electrode, electrode pads 150 d and 170 d, which have negative poles immediately adjacent or proximate the positive pole of electrode pad 150 c, may be considered to be not candidates for measuring and/or energization for that particular treatment cycle, since they are leakage-inducingly proximate to the designated primary electrode. Additionally, in this embodiment, electrode pad 150 b, which may have a positive pole immediately adjacent or proximate the negative pole of electrode pad 150 c, may be considered to not be a candidate, since it may also be leakage-inducingly proximate to the designated primary electrode. Furthermore, in this particular embodiment, electrode pad 170 b may also be considered a non-candidate because it may be on the same flex structure as the leakage-inducingly proximate electrode pad 150 b. Finally, in this particular embodiment, electrode pads 150 a and 170 a may be considered candidates because they are adjacent non-candidates.

As another non-limiting example, in some monopolar electrode embodiments, the candidate electrodes may be the monopolar electrodes that have similar measured or estimated electrical circuit properties to one or more measured or estimated properties of the electrical circuit associated with the primary electrode. In other words, in some monopolar systems, it may be desirable to only simultaneously energize monopolar electrodes that define substantially similar electrical circuits to the electrical circuit defined by the primary monopolar electrode (e.g. the circuit defined by the monopolar electrode, the common electrode, and a pathway through the patient's tissue). In some instances, this may facilitate uniformity in current flow during energization. In other embodiments, a pre-defined table or other listing or association may determine which electrodes are candidate electrodes based on the current primary electrode.

In at least some embodiments, switches associated with non-candidates may be opened to isolate the non-candidates from the rest of the system's circuitry. This switching, in at least some embodiments, may also or alternatively be used to otherwise maximize the number of available electrode pairs available for energization provided that a common ground between pairs is not affected by the switching off.

In other embodiments, the ablation device may be configured to avoid the potential for leakage or otherwise take such leakage into account, and, accordingly, all the electrodes of the device may be candidates for energization and/or measuring during a treatment cycle.

In some embodiments, the assignment of an electrode as either the primary electrode, candidate, or non-candidate may be determined by a sequence matrix or look up table in an array that identifies the status of each of the electrodes and an order for the designation of primary electrodes. In one non-limiting embodiment, the primary electrode designation cycles circumferentially through the proximate electrodes and then circumferentially through the distal electrodes (e.g. in FIG. 3, the sequence may be 170 a, b, c, d, 150 a, b, c, d). However, any pattern or other methodology could be used including ones that optimize distance between the next in sequence, the nearness of next in sequence, or the evenness of distribution.

In some embodiments, additional conditions may result in a particular electrode being set to off for a particular treatment cycle and/or for the remainder of the treatment. For instance, as discussed below, during the course of treatment, as much as 4° C. temperature overshoot may be allowed (e.g., even if such overshoot results in the electrode not being energized, it may not necessarily be set to off and may still be available for measuring); however, in at least some embodiments, if eight consecutive treatment cycles measure temperature overshoot for a particular electrode, that electrode may be set to off for the remainder of the treatment, with the treatment otherwise continuing and without otherwise changing the control loop process discussed below.

At a next step, target voltages for each of the primary and other candidate electrodes may be determined. In some embodiments, a target voltage for a particular electrode may be determined based on a temperature error associated with the treatment site of that electrode as well as the last target voltage calculated (although not necessarily applied) for that electrode. Temperature error may be calculated by measuring the current temperature at the treatment site (e.g. utilizing the temperature sensor associated with the electrode proximate that treatment site) and determining the difference between the measured temperature and the target temperature for that instant of time in the treatment.

Those of skill in the art will appreciate that while some embodiments are described as using voltage as a control variable, power could be used as an alternative to voltage for the control variable, based on, for instance, a known relationship between power and voltage (i.e. power equaling voltage times current or impedance).

One embodiment may include a sub-routine for determining a target voltage for an electrode. For example, one step may include calculating a temperature error from target (T_(e)) by subtracting the target temperature at that time (T_(g)) from the actual temperature (T) (e.g. as measured by a thermistor associated with that electrode). Subsequently, it may be determined whether the temperature error calculated at the calculating step is greater than 4° C. (i.e. if the target temperature is 68° C., determining if the temperature as measured by the thermistor is above 72° C.). If the temperature error is greater than 4° C., the sub-routine may assign that electrode a target voltage of zero for that treatment cycle. If the temperature error is not greater than 4° C., the subroutine may proceed to a next step and determine whether the temperature error is greater than 2° C. If the temperature error is greater than 2° C., the sub-routine may assign that electrode a target voltage of 75% (or another percentage) of the last assigned target voltage for that electrode. If the temperature error is not greater than 2° C., the sub-routine may assign a target voltage for that electrode based on the equation:

V=K _(L) V _(L) +K _(P) T _(e) +K _(I)∫^(t) _(t-n sec) T _(e AVE)

-   -   where:         -   V is the target voltage;         -   T_(e) is a temperature error from target;         -   V_(L) is the last assigned electrode voltage;         -   K_(L), K_(P), and K_(I) are constants; and         -   n is a time value ranging from 0 to t seconds.

In some embodiments, the equation used may be:

V = 0.75  V_(L) + K_(p)T_(e) + K_(I)∫_(t − n  sec )^(t)T_(e  AVE) 

-   -   where:         -   V is the target voltage;         -   T_(e) is the temperature error from target;         -   V_(L) is the last assigned electrode voltage;         -   K_(P) is a constant from proportionate control; and         -   K_(I) is a constant from integral control.

In some embodiments, it may be beneficial to use only the last assigned electrode voltage for determining a target voltage, rather than utilizing averages of voltages or voltages from earlier treatment cycles, as, in some cases, use of earlier voltages may be a source for computational error in embodiments that focus on fine control of the target temperature.

Once target voltages are determined for the primary electrode and other candidate electrodes, it may be determined whether the target voltage for the primary electrode is greater than zero. If not, the output voltage of the RF generator may be set for that treatment cycle to the lowest target voltage determined for the other candidate electrodes. If the target voltage determined for the primary electrode is greater than zero, the output voltage of the RF generator may be set for that treatment cycle to the target voltage of the primary electrode.

Next, the primary and other candidate electrodes with a target voltage greater than zero may be identified as electrodes to be energized. In alternative embodiments, candidate electrodes other than the primary may only be energized if the target voltages determined for those electrodes is 6V greater than the set voltage. In some embodiments, candidate electrodes other than the primary may only be energized if the target voltages determined for these electrodes are 1, 5 or 10V greater than the set voltage.

Lastly, it may be determined whether the electrodes to be energized are currently at temperatures greater than 68° C. Those electrodes that are at temperatures greater than 68° C. may be switched off or otherwise prevented from being energized in that treatment cycle, and those electrodes otherwise meeting the above criteria may be energized at the set voltage. Subsequently, another treatment cycle begins, and the control method may be repeated until the treatment is complete. In some embodiments, each treatment cycle will be non-overlapping with the previous and next cycles (e.g. the steps of the control method will be completely performed before the next cycle's steps begin), although, in other embodiments, the cycles may be overlapping at least to some extent.

Turning now to FIG. 7, a renal nerve ablation device 300 may include an expandable member 130 that may be disposed at, on, about, or near a distal region of the elongate tubular member or catheter shaft 122, as discussed above. In some embodiments, the proximal waist 136 of the expandable member 130 may be fixedly attached to the elongate tubular member or catheter shaft 122. In some embodiments, the renal nerve ablation device 300 includes a ride-along electrode support 305 with one or more electrodes. In some embodiments, the electrode support 305 may be fixedly attached to the elongate tubular member or catheter shaft 122. The electrode support 305 may be free from attachment to the body 135 of the expandable member 130. In some embodiments, the electrode support 305 may be expandable from a collapsed delivery state to an expanded state, such as a basket or a plurality of struts or elongate members, for example. The electrode support 305 may include one or more flexible elongate members 310 each having a proximal end 320 which may be fixedly attached to the catheter shaft 122. In some embodiments, a plurality of elongate members 310 have proximal ends 320 fixedly attached to the catheter shaft 122. In some embodiments, the distal ends 315 of the elongate members 310 are free of any attachment to the catheter shaft 122 and expandable member 130. In other embodiments, the distal ends 315 may be connected to each other, as shown in FIG. 7, and/or to a connection member or ring (not shown). In some embodiments, elongate members 310 are free from attachment to the catheter shaft 122 or to the expandable member 130 at least from a point distal of the proximal ends 320 and extending to the distal ends 315. The elongate members 310 may be connected to the catheter shaft 122 and unconnected to the expandable member 130. In some embodiments, proximal ends 320 of the elongate members 310 may be attached to the proximal waist 136 of the expandable member 130 in a region of connection between the proximal waist 136 and the catheter shaft 122.

In some embodiments, the electrode support 305 is a separate element from the expandable member 130 and is unconnected to the expandable member 130. As shown in FIG. 8, the electrode support 305 may be fixedly connected to a separate elongate element or catheter shaft 322. In some embodiments, the electrode support 305 may be deliverable separately from the expandable member 130. In this embodiment, the electrode support 305 may be delivered to a body lumen, followed by delivery of the expandable member 130 through catheter 322. Once the expandable member 130 is positioned within the electrode support 305, the expandable member 130 is expanded thereby expanding the electrode support 305 and placing the electrode assemblies 325 on the electrode support 305 in contact with the interior of the body lumen. Following treatment with the electrode assemblies 325, the expandable member 130 may be contracted. The lack of attachment between the electrode support 305 and the majority of the expandable member 130 allows the expandable member 130 to be deflated in any manner. For example, the expandable member 130 may be deflated via a vacuum source, re-folded or twisted by applying torque to at least a portion of the expandable member 130, or by being withdrawn back into a guide catheter 14. The contracted or deflated expandable member 130 may be withdrawn first followed by withdrawal of the electrode support 305. Alternatively, the contracted expandable member 130 and the electrode support 305 may be removed simultaneously. The separate electrode support 305 does not interfere with deflation, contraction, twisting, or re-folding of the expandable member 130. The elongate members 310 collapse into their pre-expansion state for withdrawal into a guide catheter 14.

In some embodiments, the electrode support 305 is disposed over the expandable member 130 and expands when the expandable member 130 is expanded. The elongate members 310 are not attached to the expandable member 130 and during expansion the elongate members 310 move farther apart from each other. In some embodiments, the electrode support 305 may be used with a variety of sizes of expandable member 130. The elongate members 310 move farther apart as the diameter of the expandable member 130 increases. Expansion of the expandable member 130 within a body lumen forces the elongate members into contact with the inner walls of the body lumen. Upon contraction of the expandable member 130, the electrode support 305 may remain in substantially the expanded configuration, allowing the expandable member 130 to contract, twist, fold, or otherwise attain a configuration suitable for retraction into a delivery sheath or catheter. The unattached electrode support 305 does not interfere with expansion and contraction of the expandable member. In some embodiments, the electrode support 305 collapses or folds onto the previously folded or collapsed expandable member 130 as the entire ablation device 300 is retracted into a delivery sheath or catheter when the catheter 122 is withdraw proximally. In other embodiments, the expandable member and electrode support 305 are withdrawn in order to collapse both elements substantially simultaneously. In other embodiments, the electrode support 305 may be biased in a collapsed configuration, such that when the expandable member 130 is contracted, the electrode support 305 automatically returns to a contracted configuration.

The electrode support 305 may include a plurality of electrode assemblies 325. In some embodiments, each elongate member 310 may contain one or more electrode assemblies 325. In some embodiments, each electrode assembly 325 may include a ground electrode 330, an active electrode 335, and a sensor element 340. In some embodiments, each elongate member 310 may have electrode assemblies 325 that extend from alternating sides, as shown in FIG. 7. In some embodiments, the electrodes and sensors of each electrode assembly 325 may be arranged as shown in FIG. 4. In some embodiments, the electrode support 305 may be made up of one or more elongate members 310 extending generally parallel to the longitudinal axis of the expandable member 130, as shown in FIG. 7. In other embodiments, the elongate members 310 may be twisted or canted at an angle from the longitudinal axis.

In some embodiments, the expandable member 132 has one or more channels 134 extending along a length of the expandable member 132. The channels 134 are configured to remain when the expandable member 132 is expanded. When the expandable member 132 is placed within a body lumen such as a blood vessel, and expanded, the channels 134 allow partial fluid flow across the expandable member 132. The channels 134 may be substantially parallel to a longitudinal axis of the expandable member 132, or the channels may be arranged in other configurations. In the embodiment illustrated in FIGS. 9-11, an expandable member 132 has three channels 134 extending in a spiral along the expandable member 132. Any number of channels 134 may be included in the expandable member 132. The channels 134 may be spaced apart in a manner that allows for the elongate members 360 of the electrode support 355 to be disposed between channels 134. In some embodiments, the elongate members 360 extend in a spiral matching the angle of the channels 134.

Turning now to FIG. 12, in some embodiments, a renal nerve ablation device 400 may include a ride-along electrode support 405 in which a plurality of flexible elongate members 410 extend around an expandable member 130 at an angle with respect to the longitudinal axis. As discussed above, the expandable member 130 may be disposed at, on, about, or near a distal end of the elongate tubular member or catheter shaft 122. In some embodiments, the electrode support 405 may be fixedly attached to the elongate tubular member or catheter shaft 122, and free from attachment to the body 135 of the expandable member 130. In some embodiments, the electrode support 405 may be expandable from a collapsed delivery state to an expanded state. The electrode support 405 may include one or more electrode assemblies 425. The electrode assembly 425 may include a plurality of flexible elongate members 410 with proximal ends 420 fixedly attached to the catheter shaft 122. In the embodiment illustrated in FIG. 12, the electrode assembly 425 has three elongate members 410 connected to each other only at their proximal ends 420. The distal ends 415 of the elongate members 410 may be free of any attachment to each other and to the expandable member 130. In some embodiments, proximal ends 420 of the elongate members 410 may be attached to the proximal waist 136 of the expandable member 130 in a region of connection between the proximal waist 136 and the catheter shaft 122.

In some embodiments, the electrode support 405 is disposed over the expandable member 130 and expands when the expandable member 130 is expanded. The elongate members 410 are not attached to the expandable member 130 and during expansion the elongate members 410 move farther apart from each other. The electrode support 405 may include a plurality of electrode assemblies 425. In some embodiments, each electrode assembly 425 includes a plurality of elongate members 410.

In some embodiments, each electrode assembly 425 may include three elongate members 410. A first elongate member 410 may carry a plurality of ground electrodes 430, a second elongate member 410 may carry a plurality of active electrodes 435, and a third elongate member 410 may carry a plurality of sensor elements 440. In some embodiments, the ground electrodes 430, active electrodes 435, and sensor elements 440 are grouped longitudinally on adjacent elongate members 410. In some embodiments, a single sensor element 440 may be disposed on an elongate member 410 between a first elongate member 410 with a plurality of ground electrodes 430 and a second elongate member 410 with a plurality of active electrodes 435. In some embodiments, such as that illustrated in FIG. 12, the elongate members 410 may be twisted or canted at an angle from the longitudinal axis. In some embodiments, the electrode support 405 includes two electrode assemblies 425, positioned on substantially opposite sides of the expandable member 130. In other embodiments, the electrode support 405 includes three electrode assemblies 425 positioned at substantially equal distances from each other around the expandable member 130. In some embodiments, the elongate members 410 are substantially parallel.

In some embodiments, the axial position of groups of ground 430 and active 435 electrodes and sensor elements 440 are offset on adjacent electrode assemblies 425. For example, as shown in FIG. 12, in some embodiments, the electrode assemblies may be arranged on the expandable member 130, shown here in an expanded state, according to a pair of generally cylindrical treatment zones A and B. In other embodiments, the expandable member 130 or other components of the treatment system may include additional electrode assemblies that are not in a treatment zone or are otherwise not used or configured to deliver a treatment energy.

The treatment zones A and B and associated electrode assemblies 425 a-c are further illustrated in FIG. 13, which is an “unrolled” depiction of a portion of the electrode support 405 of FIG. 12. The treatment zones A and B may be longitudinally adjacent to one another along longitudinal axis L-L, and may be configured such that energy applied by the electrode assemblies create treatments that do not overlap. Treatments applied by the longitudinally adjacent bipolar electrode assemblies 425 a-c may be circumferentially non-continuous along longitudinal axis L-L. For example, with reference to FIG. 13, lesions created in treatment zone A may in some embodiments minimize overlap about a circumference (laterally with respect to L-L in this view) with lesions created in treatment zone B. In other embodiments, however, the energy applied by the electrode assemblies, such as the electrode assemblies shown in FIG. 13, may overlap, longitudinally, circumferentially, and/or in other ways, to at least some extent.

In some embodiments, the sensor element 440 may be disposed adjacent to the ground electrode 430 and/or the active electrode 435. In some embodiments, the ground electrode 430, the active electrode 435, and/or the sensor element 440 may extend along a length of the expandable member 130. In some embodiments, the ground electrode 430, the active electrode 435, and/or the sensor element 440 may extend along substantially a full length of the expandable member 130.

Turning to FIG. 14, in some embodiments, a renal nerve ablation device 500 may include a ride-along electrode support 505 in which a plurality of flexible elongate members 510 are disposed in a helical or spiral pattern or orientation along an outer surface of the expandable member 130. As discussed above, the expandable member 130 may be disposed at, on, about, or near a distal end of the elongate tubular member or catheter shaft 122. In some embodiments, the electrode support 505 may be fixedly attached to the elongate tubular member or catheter shaft 122 and free from attachment to the body 135 of the expandable member 130. In some embodiments, the electrode support 505 may be expandable from a collapsed delivery state to an expanded state. The electrode support 505 may include an electrode assembly 525 which may include a plurality of flexible elongate members 510 with proximal ends 520 fixedly attached to the catheter shaft 122. In the embodiment illustrated in FIG. 14, the electrode assembly 525 has three elongate members 510 connected to each other only at their proximal ends 520 and distal ends 515. In some embodiments, proximal ends 520 of the elongate members 510 may be attached to the proximal waist 136 of the expandable member 130 in a region of connection between the proximal waist 136 and the catheter shaft 122.

In some embodiments, the electrode support 505 is disposed over the expandable member 130 and expands when the expandable member 130 is expanded. The elongate members 510 are free from attachment to the body 135 of the expandable member 130 and are free from attachment to each other except at their distal 515 and proximal ends 520, allowing the elongate members 510 to move farther apart from each other during expansion. The electrode support 505 may be used in combination with expandable members 130 of varying expanded sizes. The elongate members 510 may be attached to each other at their distal 515 and proximal 520 ends. In some embodiments, the distal ends 515 of the elongate members 510 may be attached to the distal waist 137 of the expandable member 130 and the proximal ends 520 of the elongate members 510 may be attached to proximal waist 136 of the expandable member 130. In other embodiments, the distal 515 and proximal 520 ends of the elongate members 510 may be attached to the catheter shaft 122. The electrode support 505 may include a plurality of electrode assemblies 525 spaced apart axially along the electrode support 505.

In some embodiments, the electrode assembly 525 may include three elongate members 510. A first elongate member 510 may carry a plurality of ground electrodes 530, a second elongate member 510 may carry a plurality of active electrodes 535, and a third elongate member 510 may carry a plurality of sensor elements 540. In some embodiments, the ground electrodes 530, active electrodes 535, and sensor elements 540 are grouped axially on adjacent elongate members 510, as illustrated in FIG. 14. In some embodiments, a single sensor element 540 may be disposed on an elongate member 510 between a first elongate member 510 with a plurality of ground electrodes 530 and a second elongate member 510 with a plurality of active electrodes 535. In some embodiments, such as that illustrated in FIG. 14, the elongate members 510 may be twisted or canted at an angle from the longitudinal axis, forming a helix. In some embodiments, the electrode support 505 includes one or more elongate support 511 disposed in a helical or spiral pattern or orientation along an outer surface of the expandable member 130. The elongate supports 511 may balance the electrode assembly 525. The elongate supports 511 may be free of electrodes or other elements. In some embodiments, two sets of three elongate supports 511 may be present. The elongate supports 511 may be connected to each other only at their proximal and distal ends and may be free of attachment to the body 135 of the expandable member 130. The distal ends 515 of the elongate members 510 may be connected to distal ends of the elongate supports 511.

In some embodiments, the electrode support 505 includes circuitry (not shown) connected to the ground electrodes 530, active electrodes 535, and sensor elements 540. In some embodiments, the circuitry extends from each electrode proximally to the catheter shaft 122. In some embodiments, a first portion of the circuitry extends proximally along the elongate members 510 to the catheter shaft 122, and a second portion of the circuitry extends distally along the elongate members 510 to the distal ends 515 of the elongate members 510. The second portion of the circuitry may then be shifted to one or more of the elongate supports 511 and extend proximally along the one or more elongate supports 511 to the catheter shaft 122. Such a split distribution of the circuitry may allow for narrower and more flexible elongate members 510.

The ground electrode 530, the active electrode 535, and the sensor element 540 may be oriented generally parallel to each other. The helical or spiral pattern or orientation may be arranged such that a plane placed normal or perpendicular to the longitudinal axis L-L of the expandable member 130 may intersect the electrode assembly 525, the ground electrode 530, the active electrode 535, and/or the sensor element 540 at a single location such that at no location along the length of the expandable member 130 does the electrode assembly 525, the ground electrode 530, the active electrode 535, and/or the sensor element 540 overlap itself longitudinally. Other arrangements, however, are contemplated.

The helical orientation along the length of the expandable member 130 forms at least one complete (360 degree) circumferential loop within the lumen or vessel that the expandable member 130 is positioned. The electrodes provide heating at a location within the tissue surrounding the body passageway without damaging the wall of the body passageway in order to disrupt the nerves located in the tissue surrounding the body passageway wall. A helical orientation is desirable to help avoid an increased risk of stenosis that may be present when electrodes are disposed within a single plane normal to a longitudinal axis of the body passageway (i.e., a circular electrode or group of electrodes).

In some embodiments, the renal nerve ablation device 300, 400, 500 may include a single ground electrode 330, 430, 530 and a single active electrode 335, 435, 535. Accordingly, the ground electrode 330, 430, 530 and the active electrode 335, 435, 535 may combine to form a bipolar electrode pair. When the renal nerve ablation device 300, 400, 500 is energized, such as in the manner(s) described above, RF energy or other suitable energy may pass from the active electrode 335, 435, 535 to the ground electrode 330, 430, 530, thereby creating a corresponding lesion or lesions along a body passageway within which the expandable member 130 has been positioned. The sensor element 340, 440, 540 may be positioned between the ground electrode 330, 430, 530 and the active electrode 335, 435, 535. The sensor element 340, 440, 540 may include at least one temperature sensor, such as a thermistor or thermocouple, positioned on the outer surface of the expandable member 130. The at least one temperature sensor may be positioned between the ground electrode 330, 430, 530 and the active electrode 335, 435, 535, and may be configured to monitor the temperature of the target tissue, the active and ground electrodes, or both, as discussed above. In some embodiments, the at least one temperature sensor may include a plurality of temperature sensors configured to monitor the temperature of the target tissue, the active electrodes, the ground electrodes, or any combination thereof, at a plurality of locations along the length of the expandable member 130.

Turning now to FIG. 15, in some embodiments, a renal nerve ablation device 600 may include an electrode support 605 similar to that discussed above with regard to the embodiment of FIG. 14, but in which the electrode assembly 625 may lack a ground electrode, or the ground electrode may not be connected to the control unit 110, such that the active electrode 635 may form a monopolar electrode. As discussed above, the electrode support 605 may include a plurality of flexible elongate members 610 disposed in a helical or spiral pattern or orientation along an outer surface of the expandable member 130. In some embodiments, the electrode support 605 may be fixedly attached to the elongate tubular member or catheter shaft 122. In some embodiments, the electrode support 605 may be expandable from a collapsed delivery state to an expanded state. The electrode support 605 may include an electrode assembly 625 which may include a plurality of flexible elongate members 610 with proximal ends 620 fixedly attached to the catheter shaft 122. In the embodiment illustrated in FIG. 15, the electrode assembly 625 has three elongate members 610 connected to each other only at their proximal ends 620 and distal ends 615. In some embodiments, proximal ends 620 of the elongate members 610 may be attached to the proximal waist 136 of the expandable member 130 in a region of connection between the proximal waist 136 and the catheter shaft 122.

In some embodiments, the electrode support 605 is disposed over the expandable member 130 and expands when the expandable member 130 is expanded. The elongate members 610 are free from attachment to the body 135 of the expandable member 130, allowing the elongate members 610 to move farther apart from each other during expansion. The elongate members 610 may be attached to each other at their distal 615 and proximal 620 ends. In some embodiments, the distal ends 615 of the elongate members 610 may be attached to the distal waist 137 of the expandable member 130 and the proximal ends 620 of the elongate members 610 may be attached to proximal waist 136 of the expandable member 130. In other embodiments, the distal 615 and proximal 620 ends of the elongate members 610 may be attached to the catheter shaft 122. The electrode support 605 may include a plurality of electrode assemblies 625 spaced apart axially along the electrode support 605.

In some embodiments, the electrode support 605 includes one or more additional elongate members 611 disposed in a helical or spiral pattern or orientation along an outer surface of the expandable member 130. The additional elongate members 611 may balance the electrode assembly 625. The additional elongate members 611 may be free of electrodes or other elements. In some embodiments, two sets of three additional elongate members 611 may be present. The additional elongate members 611 may be connected to each other only at their proximal and distal ends and may be free of connection to the body 135 of the expandable member 130.

In embodiments utilizing a monopolar electrode, a separate common ground electrode 632 may be used. The common ground electrode 632 may be capable of being a return electrical pathway for the active electrode 635. Thus, energy may be delivered to the active electrode 635 and the common ground electrode may be the return electrical pathway. As the name suggests, the common ground electrode may be utilized as a common ground for more than one active electrode. For example, the ablation device 600 may include a plurality of active electrodes, such as in FIG. 15, and a common ground electrode may be a common ground for at least some or, in at least some embodiments, all of the active electrodes. Various embodiments are contemplated that include any suitable number of active electrodes including one, two, three, four, five, six, seven, eight, nine, ten, or more active electrodes.

Because the common ground electrode may be utilized as the return electrode for a plurality of active electrodes, the active electrodes need not have a bipolar return electrode (i.e., ground trace) paired with each active electrode. This may allow active electrodes and/or the other structures associated therewith to be constructed with a smaller size or footprint. This may desirably impact the overall construction of device. For example, smaller active electrodes may be more flexible, allow for easier contracting or folding of the electrode support when proximally retracting the ablation device, reduce the profile of the ablation device, or the like.

In use, the ablation device 300, 400, 500, 600 may be advanced through a blood vessel to a position adjacent to a target tissue (e.g., within a renal artery). In some embodiments, the target tissue may be one or more renal nerves disposed about the renal artery. When suitably positioned, expandable member 130 may be expanded from a collapsed delivery configuration to an expanded configuration. This may place the active electrode 335, 435, 535, 635 against the wall of the blood vessel. The active electrode 335, 435, 535, 635 may be activated. Ablation energy may be transmitted from the active electrode 335, 435, 535, 635, through the target tissue (where renal nerves may be ablated, modulated, or otherwise impacted), and back through the ground electrode 330, 430, 530, 630, in a bipolar configuration, or back through the common ground electrode 632, in a monopolar configuration.

The materials that can be used for the various components of the ablation device 300, 400, 500, 600 (and/or other devices disclosed herein) may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to the ablation device 300, 400, 500, 600. However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to other similar tubular members and/or expandable members and/or components of tubular members and/or expandable members disclosed herein.

The ablation device 300, 400, 500, 600 and the various components thereof may be made from a metal, metal alloy, polymer (some examples of which are disclosed below), a metal-polymer composite, ceramics, combinations thereof, and the like, or other suitable material. Some examples of suitable polymers may include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, for example, DELRIN® available from DuPont), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for example, ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers such as HYTREL® available from DuPont), polyamide (for example, DURETHAN® available from Bayer or CRISTAMID® available from Elf Atochem), elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA, for example available under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene (for example REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide (for example, KEVLAR®), polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS 50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like. In some embodiments the sheath can be blended with a liquid crystal polymer (LCP). For example, the mixture can contain up to about 6 percent LCP.

Some examples of suitable metals and metal alloys include stainless steel, such as 304V, 304L, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY® C-22®, UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400, NICKELVAC® 400, NICORROS® 400, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickel-tungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like); platinum enriched stainless steel; titanium; combinations thereof; and the like; or any other suitable material.

As alluded to herein, within the family of commercially available nickel-titanium or nitinol alloys, is a category designated “linear elastic” or “non-super-elastic” which, although may be similar in chemistry to conventional shape memory and super elastic varieties, may exhibit distinct and useful mechanical properties. Linear elastic and/or non-super-elastic nitinol may be distinguished from super elastic nitinol in that the linear elastic and/or non-super-elastic nitinol does not display a substantial “superelastic plateau” or “flag region” in its stress/strain curve like super elastic nitinol does. Instead, in the linear elastic and/or non-super-elastic nitinol, as recoverable strain increases, the stress continues to increase in a substantially linear, or a somewhat, but not necessarily entirely linear relationship until plastic deformation begins or at least in a relationship that is more linear that the super elastic plateau and/or flag region that may be seen with super elastic nitinol. Thus, for the purposes of this disclosure linear elastic and/or non-super-elastic nitinol may also be termed “substantially” linear elastic and/or non-super-elastic nitinol.

In some cases, linear elastic and/or non-super-elastic nitinol may also be distinguishable from super elastic nitinol in that linear elastic and/or non-super-elastic nitinol may accept up to about 2-5% strain while remaining substantially elastic (e.g., before plastically deforming) whereas super elastic nitinol may accept up to about 8% strain before plastically deforming. Both of these materials can be distinguished from other linear elastic materials such as stainless steel (that can also can be distinguished based on its composition), which may accept only about 0.2 to 0.44 percent strain before plastically deforming.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy is an alloy that does not show any martensite/austenite phase changes that are detectable by differential scanning calorimetry (DSC) and dynamic metal thermal analysis (DMTA) analysis over a large temperature range. For example, in some embodiments, there may be no martensite/austenite phase changes detectable by DSC and DMTA analysis in the range of about −60 degrees Celsius (° C.) to about 120° C. in the linear elastic and/or non-super-elastic nickel-titanium alloy. The mechanical bending properties of such material may therefore be generally inert to the effect of temperature over this very broad range of temperature. In some embodiments, the mechanical bending properties of the linear elastic and/or non-super-elastic nickel-titanium alloy at ambient or room temperature are substantially the same as the mechanical properties at body temperature, for example, in that they do not display a super-elastic plateau and/or flag region. In other words, across a broad temperature range, the linear elastic and/or non-super-elastic nickel-titanium alloy maintains its linear elastic and/or non-super-elastic characteristics and/or properties.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy may be in the range of about 50 to about 60 weight percent nickel, with the remainder being essentially titanium. In some embodiments, the composition is in the range of about 54 to about 57 weight percent nickel. One example of a suitable nickel-titanium alloy is FHP-NT alloy commercially available from Furukawa Techno Material Co. of Kanagawa, Japan. Some examples of nickel titanium alloys are disclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which are incorporated herein by reference. Other suitable materials may include ULTANIUM™ (available from Neo-Metrics) and GUM METAL™ (available from Toyota). In some other embodiments, a superelastic alloy, for example a superelastic nitinol can be used to achieve desired properties.

In at least some embodiments, portions of the ablation device 120 may also be doped with, made of, or otherwise include a radiopaque material. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of the ablation device 120 in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. Additionally, other radiopaque marker bands and/or coils may also be incorporated into the design of the ablation device 120 to achieve the same result.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI) compatibility may be imparted into the ablation device 120. For example, portions of device, may be made of a material that does not substantially distort the image and create substantial artifacts (i.e., gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MRI image. In some of these and in other embodiments, portions of the ablation device 120 may also be made from a material that the MRI machine can image. Some materials that exhibit these characteristics include, for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nitinol, and the like, and others.

The entire disclosures of the following documents are herein incorporated by reference in their entirety:

U.S. patent application Ser. No. 13/750,879 (Attorney Docket No. 1001.3095102), filed on Jan. 25, 2013, and entitled “METHODS AND APPARATUSES FOR REMODELING TISSUE OF OR ADJACENT TO A BODY PASSAGE”.

It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the disclosure. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention's scope is, of course, defined in the language in which the appended claims are expressed. 

What is claimed is:
 1. A medical device for renal nerve ablation, comprising: a catheter shaft; an expandable member coupled to the catheter shaft, the expandable member having a proximal region, a distal region, and a body extending therebetween; and an electrode support coupled to the catheter shaft and positioned over the body of the expandable member, the electrode support including a plurality of flexible elongate members and a plurality of electrode assemblies disposed on the elongate members, the electrode support capable of expanding with the expandable member, wherein the electrode support is free from attachment with the body of the expandable member.
 2. The medical device of claim 1, wherein each elongate member includes at least two spaced apart electrode assemblies.
 3. The medical device of claim 1, wherein the electrode support is capable of being delivered to a target site separately from the expandable member.
 4. The medical device of claim 1, wherein the electrode support includes a proximal section, wherein the electrode support and the expandable member are attached to each other only at the proximal section of the electrode support and the proximal region of the expandable member.
 5. The medical device of claim 1, wherein the electrode support has an open distal end capable of slidingly engaging the distal region of the expandable member.
 6. The medical device of claim 1, wherein the elongate members each include a proximal section, wherein the elongate members are connected to each other only at their proximal sections.
 7. The medical device of claim 1, wherein the electrode support includes two or more sets of three elongate members, wherein each set includes a first elongate member carrying active electrodes, a second elongate member including one or more temperature sensors, and a third elongate member carrying ground electrodes.
 8. The medical device of claim 1, wherein the elongate members extend along the expandable member at an angle relative to a longitudinal axis of the expandable member.
 9. The medical device of claim 1, wherein at least some of the electrode assemblies include a pair of bipolar electrodes.
 10. The medical device of claim 1, wherein at least some of the electrode assemblies include a temperature sensor.
 11. The medical device of claim 10, wherein the temperature sensor is positioned between a bottom surface of one of the electrode assemblies and an outer surface of the expandable member.
 12. The medical device of claim 1, wherein the expandable member includes one or more channels in an outer surface extending from a distal region to a proximal region of the expandable member.
 13. The medical device of claim 1, wherein the expandable member is a compliant balloon.
 14. The medical device of claim 1, wherein the expandable member is a non-compliant balloon.
 15. The medical device of claim 1, wherein the expandable member has one or more channels extending along the body, the channels positioned between the elongate members.
 16. A medical device, comprising: a catheter shaft; an expandable balloon having a distal waist, proximal waist, and a body extending therebetween, the proximal waist being coupled to the catheter shaft; a flexible elongate electrode assembly coupled to the catheter shaft and extending in a helix over the body of the expandable balloon, the electrode assembly free from attachment to the body of the expandable balloon; and a plurality of electrode elements disposed on the flexible elongate electrode assembly.
 17. The medical device of claim 16, wherein the elongate electrode assembly includes three spaced apart elongate members each having a distal region, a proximal region, and a body extending therebetween, wherein the three elongate members are free from attachment to each other along their respective bodies.
 18. The medical device of claim 17, further comprising one or more elongate supports each having a distal region, a proximal region, and a body extending therebetween, the elongate supports extending in a helix over the body of the expandable balloon and spaced apart from the elongate members, the elongate supports connected to the elongate members only at their distal and proximal regions.
 19. The medical device of claim 18, further comprising circuitry connected to the electrode elements, wherein a first portion of the circuitry extends proximally along a first elongate member on which the electrodes reside, wherein a second portion of the circuitry extends distally along the first elongate member to a first elongate support, the second portion of the circuitry then extending proximally along the first elongate support.
 20. A method for treating hypertension, the method comprising: providing a medical device, comprising: a catheter shaft, an expandable member coupled to the catheter shaft, an expandable electrode support coupled to the catheter shaft and positioned over the expandable member, the electrode support including a plurality of flexible elongate members and a plurality of electrode assemblies disposed on the elongate members, the electrode support capable of expanding with the expandable member, wherein the electrode support is free from attachment with the expandable member, and a delivery sheath; advancing the medical device through a blood vessel to a position within a renal artery; expanding the expandable member, thereby expanding the electrode support; energizing the electrode assemblies; collapsing the expandable member, and thereafter, withdrawing the expandable member and the electrode support into the delivery sheath, thereby collapsing the electrode support. 